Fabrication Of Extended Heterocyclic Aromatic Semiconducting Molecules And Their Applications In Photoelectric Functional Materials

In recent years,photoelectric functional materials with well-defined structures have drawn great attention as materials for a variety of electronic and optoelectronic devices such as organic and polymeric light emitting diodes,field effect transistors and photovoltaic cells.Among them,molecular functional materials,especially those?-conjugated semiconductors are attractive semiconducting components for a number of optoelectronic applications,particularly because of their well-defined chemical structures,better solubility,easier purification method,lower cost,fewer defects,and faster charge mobility comparing to traditional inorganic semiconductor materials.Therefore,rational design and synthesis of extended heterocyclic aromatic compounds for constructing ?-conjugated semiconductors are very urgent issues.Among the classes of ?-conjugated compounds,nitrogen-containing heterocycles are very promising building blocks to synthesize a great number of photoelectric materials.1,10-Phenanthroline,as a type of common electron-deficient group,is often fused with electron-rich thiophene rings and bridged by imidazole groups.Hence 2-(2-thienyl)imidazo[4,5-f][1,10]-phenanthroline(TIP)as a typical donor-acceptor molecule was formed.Moreover,TIP derivatives can be used as the ancillary ligands to produce corresponding ruthenium sensitizers for dye-sensitized solar cells(DSSCs).This paper mainly contains two parts of work.The first part was about the design and synthesis of TIP based aromatic heterocyclic ligands and their corresponding ruthenium sensitizers.The second was related to a series of organic semiconductors,their crystal structures,synthetic methods and photoelectric properties.The details were shown as follows:In Chapter 1,the research background of this thesis has been described,which mainly involves the classification,extending methodology and optoelectronic properties of ?-conjugated molecular materials.The aim was to understand the structure-function relationship in ?-conjugated molecular materials,which could help us to prepare new high-performance optoelectronic materials and devices.In Chapter 2,four new ruthenium sensitizers(S1-S4)were synthesized via a step-by-step synthetic strategy via their respective precursors(D1-D4),where 2-thiophenimidazo[4,5-f][1,10]phenanthroline based ancillary ligands were presented with different substituents at a and ? positions of the thiophene unit.It was found that the introduction of an electron-deficient radical at ? positions of the thiophene unit in the ancillary ligand had a positive influence on the efficiency of the final dye-sensitized solar cells,where sensitizer S3 showed the best overall power-conversion efficiencies in this group of ruthenium sensitizers(4.95%compared to 6.07%for sensitizer N3).In Chapter 3,a pair of isomeric ruthenium sensitizers BM1 and BM2,having TIP based ancillary ligands with a 9-phenylcarbazole tail at a or ? position of the thiophene unit,was introduced to fabricate DSCs.Distinguishable photovoltaic performance were observed from the test results.(PCEs:7.33%and 5.33%for BM1 and BM2 as compared with 6.07%for standard N3-dye).In Chapter 4,three new imidazo[5,4-f]2,7-di-tert-butyl-pyrene-imidazol derivatives were prepared from 2,7-di-tert-butylpyrene-4,5,9,10-tetraone and respective aromatic aldehydes through Debus-Radziszewski reaction.It is noted that three pairs of cis and trans isomers can be separated after double imidazole N-alkylation for the central fused imidazole/pyrene/imidazole core,because of their distinguishable molecular polarity and improved solubility.Successful separation of every cis and trans isomeric pair can be evidenced by the single-crystal structural and spectral proofs.To the best of our knowledge,the current study was the first structural and spectral investigation on the imidazole N-alkylation of imidazole/pyrene/imidazole based compounds after successful separation of cis and trans isomers.In Chapter 5,two small molecular chromogenic sensors MS-1 and MS-2 for acid-base discoloration and optoelectronic investigations were synthesized and characterized.After coordination with acid,the colour of the solution and powder changed obviously which could be easily observed by the naked eye.Furthermore,the crystal conductivity of MS-1 could be significantly improved after treating with acid gas.On the other hand,MS-2 showing relatively good film-forming ability was used as a hole transport material(HTM)in perovskite solar cells,exhibiting a power conversion efficiency(PCE)of 6.68%.As far as we know,it was the first demonstration of effective perovskite solar cells based on the HTMs of Schiff-base structure.